Scope the search fields

The in qualifier limits what fields are searched. With this qualifier you can restrict the search to the username, public email, full name, or any combination of these. Without the qualifier, only the username and email address are searched. For privacy reasons, you cannot search by email domain name.

Search based on when a user joined GitHub Enterprise

You can filter users based on when they joined with the created qualifier. This takes a date as its parameter. Date formatting must follow the ISO8601 standard, which is YYYY-MM-DD (year-month-day).
You can also add optional time information THH:MM:SS+00:00 after the date, to search by the hour, minute, and second. That's T, followed by HH:MM:SS (hour-minutes-seconds), and a UTC offset (+00:00).